The swordfish is classified as Least Concern (LC) on the IUCN Red List. The North Atlantic stock is classified as Endangered (EN) (1).

A fast-swimming predator, the swordfish (Xiphias gladius) gets its name from its extremely long, flat, sword-like bill, which is used to impale or slash its prey. The swordfish, the only living member of the family Xiphiidae (3), has a long, cylindrical blackish-brown body that gradually fades to light-brown on the underside (2). The body tapers to large anal fins, which along with the high dorsal fin enable efficient cruising. Adult swordfish are scaleless and possess no teeth; swordfish less than one meter in length have small spines on the body and fine, file-like teeth (2). Usually, female swordfish grow larger and live longer than males (2) (3).

The swordfish occurs in tropical, temperate and sometimes even cold waters of all oceans, primarily between 50°N to 50°S (2) (3).

An oceanic species, the swordfish is usually found in mid-water, at depths from 200 to 600 metres, in water from 18 to 22°C. It is frequently seen swimming at the surface, but may also swim at depths greater than 650 metres (2) (4).

Swordfish have evolved to be formidable predators. They possess acute eyesight, with which they can locate prey, and their flesh consists primarily of ‘white’ muscle which provides energy for sudden bursts of activity, such as when in pursuit of their quarry (3). The swordfish then uses its bill to stun or impale its victim, slashes it into pieces or swallows it whole (3) (5). Swordfish feed during the day (3), primarily on squid, but also fish and occasionally crustaceans (6) (7) (8). They undertake vertical migrations in the ocean, following the movement of many small shrimp, fish and squid that move with the changing light intensity in a (somewhat unsuccessful) attempt to avoid predators (3) (7). Unlike some fish, swordfish are unable to maintain a body temperature higher than the temperature of the surrounding water. Instead, they have a unique muscle and brown tissue that warms blood flowing to the brain and eyes, enabling it to tolerate the extreme cold of the ocean depths (3).

Swordfish also undertake lengthy seasonal migrations, to temperate or cold waters in the summer where they feed, and back to warm waters in autumn for spawning (2). Unlike tuna, which have mostly ‘red’ muscle which is good for endurance activities, the mostly ‘white’ muscle of swordfish is not suited to swimming for long periods without fatigue (3). Therefore, swordfish undertake their long migrations by moving with prevailing currents (3).

Spawning occurs year-round in warm equatorial waters, while in cooler regions it occurs in the spring and summer (2) (4). The best known spawning grounds of the swordfish are found in the Mediterranean Sea, south of the Italian peninsula and Sicily (2). Swordfish eggs have been found here from June to September, and large numbers of juveniles occur throughout the Mediterranean from November to March (2). Fertilisation is external (3), whereby a female releases millions of buoyant eggs into the water, which are then fertilised by sperm secreted by the male. From the fertilised eggs hatch swordfish larvae. At only four millimetres long, with a short snout, and distinct, prickly scales (4), the larvae is vastly different to the great predator it will become. During the first year of life the larvae grow at a phenomenal rate, reaching a length of 90 centimetres (3). Female swordfish are thought to reach maturity at around 150 centimetres; whereas males are thought to mature at much smaller sizes, perhaps at around 100 centimetres (3).

Swordfish have been hunted by man for thousands of years, beginning with the harpooning of large female swordfish as they basked on the sea surface (3). Commercial fishing of this species commenced in the 1800s (3). Today, important swordfish fisheries exist in the Atlantic, Pacific and Indian Oceans (2), and the swordfish is captured incidentally in many other fisheries (3). As a result, stock assessments suggest that three out of the six established fisheries (in the Mediterranean, South Atlantic and North Atlantic) are, or have been, fished at unsustainable levels (3).

Swordfish abundance in the North Atlantic has shown a continuous decline since about 1980 (3), resulting in the IUCN classifying this stock as Endangered (1). In the Mediterranean, total catch levels and the size composition of the swordfish catch has also declined significantly (3).

As well as commercial fishing, the swordfish is threatened by being a prized catch of recreational anglers (3).

The International Commission for the Conservation of Atlantic Tuna (ICCAT), formed in 1969 to protect populations of tuna, swordfish, marlin, and other large ocean-going commercially fished species (9). In 1999, ICCAT introduced a ten year recovery plan to rebuild the North Atlantic swordfish stocks (10). The plan, involving strict fishing quotas, has been a great success, with signs of improved catch rates within just two years (3). The United States also took steps to protect North Atlantic swordfish stocks by closing swordfish nursery areas to fishing (4) (10). This remarkable recovery highlights the importance of accurate stock assessments and careful fisheries management, actions that will hopefully be undertaken on the lesser known stocks in the future.

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Anal fins: in fish, an unpaired fin on the under surface of a fish, behind the anus.

Crustaceans: diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, slaters, woodlice and barnacles.

Dorsal fin: the unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans.

Fertilisation: the fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.

Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.

Spawning: the production or depositing of large quantities of eggs in water.

Nakamura, I. (1985) Billfishes of the World. An annotated and illustrated catalogue of marlins, sailfishes, spearfishes and swordfishes known to date. Food and Agriculture Organization of the United Nations, Rome.